Method of producing a laminated thermoplastic foam-film receptacle

ABSTRACT

A disposable plastic dish comprised of a thin lamina of thermoplastic film superimposed upon a thermoplastic foam lamina is produced by thermoforming a substantially uniform thickness laminated stock material within complementary shaped male and female mold parts to produce a dish having an outwardly extending tapered rim at its upper periphery, the foam of the rim being compressed to a greater density than the foam of the remainder of the dish to strengthen the edge of the dish. The stock material is preferably preheated prior to thermoforming.

Julyv 2, 1914 o. A. HAASE 3 KETHOD OF PRODUCING A LAMINATEDTHERMOPLASTIC FOAM-FILM RECEPTACLE Original Filed Jan. 5, 1971 FIG.1'

United States Patent 01 hee 3,822,161 Patented July 2, 1974 3,822,161METHOD OF PRODUCING A LAMINATED THERMOPLASTIC FOAM-FILM RECEPTACLEDonald Andrew Haase, Penfield, N .Y., assignor to Mobil Oil Corporation,New York, N.Y.

Original application Jan. 5, 1971, Ser. No. 104,046, now Patent No.3,684,633. Divided and this application May 23, 1972, Ser. No. 256,135

Int. Cl. B29c 17/10 US. Cl. 156-245 6 Claims ABSTRACT OF THE DISCLOSUREA disposable plastic dish comprised of a thin lamina of thermoplasticfilm superimposed upon a thermoplastic foam lamina is produced bythermoforming a substantial- 1y uniform thickness laminated stockmaterial within complernentary shaped male and female mold parts toproduce a dish having an outwardly extending tapered rim at its upperperiphery, the foam of the rim being compressed to a greater densitythan the foam of the remainder of the dish to strengthen the edge of thedish. The stock material is preferably preheated prior to thermoforming.

CROSS-REFERENCE TO RELATED APPLICATION This application is a division ofmy copending application Ser. No. 104,046 filed Jan. 5, 1971, now US.Pat. No. 3,684,633, which claims a product which may be produced by themethod claimed in the instant application.

BACKGROUND OF THE INVENTION The present invention relates to a methodfor producing receptacles for food for human consumption, and moreparticularly to laminated thermoplastic dishes, e.g., plates, bowls andsaucers. The dishes of the invention are made from a thermoplastic foaminsulating lamina and a thin inner reinforcing lamina of a thermoplasticfilm. It is also contemplated that a second reinforcing film may beprovided on the other side of the foam insulating lamina.

It is well known in the prior art to employ disposable dishes made of apaper stock which may be coated or uncoated. Paper stock of this type issubject to mechanical deterioration and disintegration, particularlywhen the dish contains an aqueous liquid, for example if the dish has aglued seam, the seam may weaken or break. The use of coated paper issubject to the disadvantage of possible contamination of the foodproduct by the coating material.

In view of these problems it has also been proposed to make disposabledishes of one or more layers of syn thetic plastic material.Constructing such dishes solely of a thermoplastic foam such as foamedpolystyrene is not feasible since although the foam is a light-weightrigid material having very good insulating properties which aredesirable in a product of this nature, the foam does not have suflicientstructural strength unless a very thick sheet of foam is employed. Adish of relatively thick foam is undesirable from both an economicstandpoint and an aesthetic standpoint. Making the dishes of arelatively strong thermoplastic film is undesirable since such disheswould not have the desirable insulating properties, and it would lackrigidity unless a relatively thick film was employed.

In view of the foregoing, it has been proposed to construct dishes of acombination of a thermoplastic foam and a thermoplastic film in order tohopefully obtain a product which has the desirable characteristics ofeach without their shortcomings. However, known prior art laminatedplastic foam-film dishes have generally not achieved good consumeracceptance.

A principal reason for negative consumer reaction has been that, ingeneral, when thermoforming and trimming plastic foam-film laminates itis normal for the thickness of the foam in the trim area, whichcorresponds to the periphery of the dish, to be near the same thicknessor gauge as the balance of the laminate. Thus the thickness of the foamat the edge of the finished dish remains substantially the same as thethickness of the remainder of the dish. While certain types of trimmingoperation will reduce this thickness somewhat, the finished dish willnevertheless evidence a substantial thickness at the trimmed edge. Inthe case of a thermoformed plastic foam-film laminate, that is, alaminate of dissimilar materials, the trimmed edge will reveal theStratified layers of materials comprising the laminate. It has beenfound that consumer reaction is negative to such a thick edge onthermoformed foam-plastic laminated tableware articles such as plates,bowls, saucers, etc. in view of what consumers apparently consider to bean aesthetically unattractive appearance.

SUMMARY OF THE INVENTION It is a principal object of the presentinvention to provide a novel method for producing a thermoplastic foamfilm laminated dish which is not subject to the aforementioned adverseconsumer reaction exhibited towards prior art dishes of this generaltype, and which has good strength characteristics.

In order to accomplish the objectives of the present invention, duringthe course of thermoforming the laminated stock material from which thedish is made, the gauge of the thermoplastic foam at the peripheral edgeof the resulting dish is substantially reduced by compressing thisportion of the foam. Ideally, the thickness of the foam tapers towardsthe periphery to the lower limit of the gauge which would result fromcomplete compression of the foam. In addition, the dish is formed withan outwardly extending peripheral rim so that when viewed from above theobserver does not see the trimmed peripheral edge of the dish. The rimwhen seen in vertical cross-section preferably has an arcurate,downturned configuration.

Besides the improved appearance resulting from the above-mentionedconstruction, it has been found that the compression and reduction incross-section of the foam at the rim of the dish results in a change inthe physical strength properties of the foam. The ultimate elongation ofpolystyrene foam as measured in a standard tensile test increases as thefoam is compressed to smaller gauges. Accordingly, the provision of sucha compressed edge on a polystyrene foam dish such as a dinner plateresults in the advantage that the dish can deflect further under loadbefore failing. This increased resistance of the edge of the dish tocracking and the like is particularly advantageous since failure of thistype of product nearly always occurs with propagation of a break whichbegins at the edge of the product.

A dish in accordance With the presently preferred embodiment of thepresent invention is comprised of a polystyrene foam lamina upon whichthere is heat sealed a thin lamina of biaxially oriented polystyrenefilm which comprises the upper surface of the dish, that is, the surfacewhich directly contacts the food. The thickness of the film issubstantially uniform throughout, and the thickness of the foam issubstantially uniform throughout with the exception of the foam at theperipheral rim which is compressed into a tapering configuration toachieve the pleasing appearance and increased resistance to cracking andthe like discussed previously.

3 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a dishwhich is in accordance with the presently preferred embodiment of theinvention.

FIG. 2 is a vertical sectional view taken on the line 2-2 of FIG. 1.

FIG. 3 is a view similar to FIG. 2 of another embodiment of the presentinvention.

FIG. 4 is a vertical cross-sectional view through one side of apparatusfor thermoforming and trimming a laminated stock material to obtain thedish of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawing,reference numeral generally designates a dish constructed in accordancewith the presently preferred embodiment of the invention. For purposesof illustration, the invention has been depicted as embodied in a dinnerplate, but the invention is also applicable to other dishes such assaucers and bowls.

The dish 10 is constructed of an outer insulating and rigidifying lamina12 of polystyrene film and an inner strengthening lamina 14 of anoriented thermoplastic film preferably biaxially oriented polystyrenefilm. The thickness of the polystyrene foam lamina 12 is relativelyuniform throughout the generally horizontal base and the upwardly andoutwardly sloping annular side of the plate. The dish has an arcuatedownturned peripheral rim which is constituted by a peripheral edgeportion 16 of the foam and by the overlying edge of the film 14.

As seen in FIG. 2, the foam edge portion 16 tapers outwardly to an edgethickness which is only a small fraction of the thickness of the foamlamina 12 constituting the remainder of the dish. The foam of edgeportion 16 is compressed with the degree of compression varyinginversely with the thickness, that is the greatest amount of compressionoccurs at the edge of the rim portion 16.

While exact dimensions such as thickness will vary depending upon theoverall size of the dish and its configuration, the thickness of thefilm 14 is normally 1-10 mils, preferably about 2-4 mils, and thethickness of the foam lamina 12 is preferably within the range of 60 to110 mils. The density of the foam is normally in the range of 3 to 6pounds per cubic foot except at the rim where the foam is compressed toabout 10 to 50 and preferably 30 to 50 pounds per cubic foot. Thethickness of the foam edge portion 16 is preferably within the range of10 to 30 mils. The amount of reduction in thickness occurring in the rimportion 16 is at least 50% and preferably about 70 to 90% based on thethickness of the foam lamina 12 immediately adjacent to the edge portion16.

In view of the relatively small thickness of the foam edge portion 16and in view of the rim configuration, the joint between the stratifiedlaminae 12 and 14 is relatively unnoticeable, and this is especiallytrue when the plate is seen in plan view as would be the case when theplate is in use upon a table.

In order to improve the appearance of the dish, the foam may be coloredby the addition of a suitable pigment prior to extruding the foam. Thiscolor will be visible through the transparent or translucent biaxiallyoriented polystyrene film 14. If desired, a suitable design may beimprinted upon the inside of the dish during or after the step ofthermoforming the dish.

FIG. 3 illustrates another embodiment of the present invention which isidentical to the embodiment described previously with the exception thatin the FIG. 3 embodiment an additional oriented thermoplastic film,preferably a biaxially oriented polystyrene film, is provided as anouter lamina 18 on the underside of the dish.

The FIG. 3 embodiment is presently a less preferred embodiment of theinvention than that of FIG. 1. Although the film lamina 18 impartsadditional strength to the dish, this additional strength is normallynot required in most applications. Similarly although the outer lamina18 improves the appearance of the underside of the dish, this isnormally not significant since the user is concerned primarily with theappearance of the dish in use. At this time it is the upper surface ofthe dish, that is, the surface covered by the film lamina 14 which isseen by the user. Accordingly, the additional expense of providing theouter lamina 18 is normally not warranted. Nevertheless, there may beoccasions when the provision of the outer lamina is warranted.

The dishes of the invention are prepared from a stock materialcomprising a laminated web of substantially uniform thickness comprisinga lamina of polystyrene foam and a lamina of thermoplastic film heatsealed to one side of the foam lamina, or in the case of the FIG. 3embodiment there is also a lamina of thermoplastic film heat sealed tothe outer side of the foam lamina.

The laminated stock material is preferably prepared without the use ofan adhesive by heat sealing the preformed laminae to each other. Thepolystyrene foam lamina may be prepared employing a standard extruderhaving a tubular die orifice to extrude a tube of polystyrene foam.Essentially conventional extrusion techniques may be utilized to producethe polystyrene foam, for example, the foam may be prepared by extrudingpolystyrene beads which have a blowing agent such as pentaneincorporated therein. Alternatively, a direct injection extrusiontechnique may be employed whereby polystyrene resin pellets areintroduced into a standard extruder and, as the polystyrene is formedinto a molten mass within the confines of the extruder, a blowing agentsuch as pentane or other normally liquid low boiling hydrocarbon isinjected into the molten mass. Thereafter, the pentane-moltenpolystyrene mixture is extruded through a tubular die orifice. Theresulting polystyrene foam tube may be drawn over a mandrel andsubsequently cut longitudinally and flattened to form a fiat polystyrenefoam sheet. While still hot the foam sheet is heat sealed to thethermoplastic film, for example, biaxially oriented polystyrene filmwhich has been pre heated preferably to about F. The heat sealing isaccomplished using a heated seal roll maintained at a temperature ofabout 250 F. to about 350 F. preferably from about 290 F. to about 320F. This interface temperature is effective to cause heat sealing sinceresidual blowing agent present in the foam has a plasticizing orsoftening effect upon the foam so that the lamination may be carried outat temperatures lower than that conventionally utilized in the heatsealing of such materials. Usually the laminated stock material isallowed to age, for about one to two days prior to thermoforming, but insome installations the thermoforming may be carried out directlyfollowing the laminating step.

FIG. 4 illustrates the basic apparatus used for both molding and cuttingthe stock material into a dish. For purposes of illustration, the dishshown is a dinner plate con- .structed in accordance with the embodimentof FIG. 1.

The plate is produced from the preheated stock material having an upperthermoplastic film lamina 14 and a lower foam lamina 12, each laminabeing initially of substantially uniform thickness throughout. Theapparatus includes complementarily shaped male and female mold parts 20and 22. As is clearly shown in FIG. 4, the configuration of the moldparts is such that the compressed rim portion 16 is obtained bycompression of the foam in this region. It will of course be appreciatedthat the stock material may be of such size that a plurality of moldsmay act upon the stock material at the same time in order tosimultaneously produce a plurality of dishes. At the conclusion of thethermoforming operation, the excess or scrap portion of the stockmaterial indicated by reference numeral 24 is cut off by a forged knife26 which compresses the foam and shears it against a cutting anvil 28.Preferably the knife 26 is heated to a temperature which may be as highas about 250 F. While this is helpful to achieving the desired thin edgeon the final product, it is not essential. The dish is then removed fromthe mold in conventional manner.

EXAMPLE A 9 inch diameter dinner plate was prepared'from a laminatedstock material comprising a lamina of 3.0 gms./ 36 square inch basisweight polystyrene foam containing pentane as a blowing agent, and anupper lamina of 3.0 mil printed biaxially oriented polystyrene. Thestock material was thermoformed using a Thermtrol Model 460 thermoformeremploying a former cycle of 3.5 seconds. This apparatus includes matchedaluminum molds, and the scrap stock material was cut oil. employing atrim-inplace technique. The mold was preheated to 105 F. and the stockmaterial was also preheated to about 220-230" F. which preheating causedan increase in the thickness of the foam. The finished plate, whichexhibited a small amount of spring back of the foam when the moldingpressure was removed, had a thickness of 0.090 inch and a foam densityof 3.7 pounds per cubic foot throughout except in the compressed rimportion. The thickness at the outer edge of the rim was 0.011 inch, andthe density of the rim increased progressively to the outer edge atwhich the density was 40 pounds per cubic foot. It has been found thatplates produced by this procedure are preferred by consumers as comparedto thick edge prodnets, and the plates also exhibit improved tear andbreakage resistance due to the compressed foam rim.

It will be appreciated that other dishes such as saucers and bowls areproduced similarly using appropriately contoured molds.

While presently preferred embodiments of the invention have been shownand described with particularity, it

will be recognized that various changes and modifications may readilysuggest themselves to those of ordinary skill in the art upon beingapprised of the present invention.

. For example, considerable variation may be made in the prising thesteps of introducing a sheet of stock material comprising an orientedpolystyrene film lamina superimposed upon a polystyrene foam lamina intoa mold having complementary shaped male and female molded parts,thermoforming the stock material to produce a dish having a base and anupwardly extending annular side portion, comprising the foam in an outerperipheral edge portion of said annular side portion during thethermoforming step to produce a tapering peripheral rim, said rim beingdownturned during the thermoforming step so that a stratified edge atthe juncture of the film lamina and the foam lamina is normally not seenwhen the dish is viewed from above, the density of the foam in said rimbeing at least greater than the density of the remainder of the foam,and severing the thermoformed dish from the remainder of the stockmaterial.

2. A method according to Claim 1, further comprising preheating thestock material prior to introduction of the stock material into themold.

3. A method according to Claim 1, further comprising heat sealing thethermoplastic film lamina to the thermoplastic foam lamina to producesaid sheet of stock material.

4. A method according to Claim 1, wherein the foam in .the rim portionis compressed sufficiently to materially increase the resistance of theedge of the dish to cracking.

5. A method according to Claim 1, further comprising reducing thethickness of the foam in said rim during the compression step a maximumof about -90 percent based on the thickness of the remainder of thefoam.

6. A method according to Claim 1, wherein the initial density of saidstock material is about 3 to 6 pounds per cubic foot, and the density ofthe compressed foam in said rim progressively increases to about 10 to50 pounds per cubic foot.

References Cited UNITED STATES PATENTS 2,797,179 6/ 1957 Reynolds et a1.264-163 X 3,164,655 1/1965 Howard et al. 264321 3,335,892 8/1967Hildreth 264-321 X 3,488,714 1/1970 Walters et a1 161-402 X 3,534,12810/1970 Makowski 264321 X EDWARD G. WHITBY, Primary Examiner US. Cl.X.-R.

